Zero corrector for sealed instruments



Oct. 11, 1955 F. x. LAMB 2,720,187

ZERO CORRECTOR FOR SEALED INSTRUMENTS Filed April 2, 1953 FHA/V05 X.LAMB INVENTOR.

United States Patent ZERO CORRECTOR FOR SEALED INSTRUMENTS Francis X.Lamb, East Orange, N. 1., assignor to Weston Electrical InstrumentCorporation, Newark, N. J., a corporation of New Jersey ApplicationApril 2, 1953, Serial No. 346,473

10 Claims. (Cl. 116129) This application is a continuation-in-part of mypending United States application Serial No. 213,433, filed March 1,1951, and entitled Zero Corrector For Sealed Instruments.

Although the invention described herein is adapted to numerous specificapplications wherein mechanical motion must be introduced from anexternal source into a sealed mechanism without impairing the seal, Ishall limit the description to a zero adjuster used on an electricalindicating instrument.

It is desirable that electrical instruments, especially those in whichthe mechanism is quite delicate, be sealed effectively so that themechanism is not affected adversely by humidity changes, deleteriouschemicals, gases or dust, or etc. At the same time it is desirable and,in fact, often necessary, that some means be provided to permitadjustment of the mechanical zero position of the indicating pointer, bythe user, without destroying the sealed character of the instrumentcase.

Various proposals, have been made for providing a zero-adjusterarrangement on sealed instruments. While such prior proposals accomplishthe desired purpose they are,,in general, costly to produce and/orrequire the use of a special tool for the zero-adjusting operation. Ineither case, such prior constructions have not found wide use in theelectrical instrument class.

An object of this invention is the provision of a simple motiontransmitter for sealed instruments, which transmitter does not requirethe use of a special tool and which is effective to prevent the passageof air, dust and moisture into the instrument.

An object of this invention is the provision of a sealed motiontransmitter for electrical instruments, or the like, wherein the sealingmember comprises a pressure-loaded element of resilient material.

An object of this invention is the provision of a zero adjuster forsealed instruments and comprising a rotatable head accessible from theexterior of the instrument case, an insulating member within the case, acompressible member disposedbetween the insulating member and the casewall, and means securing together the said head and the insulatingmember in such manner that the compres sible member is subjected topressure-deformation.

An object of this invention is the provision of a sealed zero adjusterfor electrical instruments comprising a rotatable member extendingthrough a wall of the instrument, an insulator member abutting againstthe opposite surface of the wall and having an axial shaft extending atleast partially through such wall, a recess in the wall, a resilientwasher disposed Within the recess, and means securing the rotatablemember to the shaft in such manner that the washer issubjected tocompressive pressure within the recess.

These and otherobjects and advantages will be apparent from thefollowing description when taken with the accompanying drawingsillustrating several embodiments of the invention. The drawings are forpurposes of illustration and are not to be construed as defining the2,720,187 Patented Oct. 11, 1955 scope or limits of the invention,reference being bad for the latter purpose to the appended claims.

In the drawings wherein like reference characters denote like parts inthe several views:

Figure l is a top plan view of one type of instrument embodying theinvention;

Figure 2 is essentially a cross sectional view taken through the zeroadjuster and drawn to an enlarged scale;

Figure 3 is an exploded view of the Figure 2 assembly;

Figure 4 is similar to Figure 2 and showing another embodiment of theinvention.

Figure 5 is a similar view of another embodiment of the invention;

Figure 6 is a front view of the rotary member shown in Figure 5 whichmember is disposed-against the inner surface of the instrument cover;

Figure 7 is a cross-sectional view showing another embodiment of theinvention; and

Figure 8 is a similar view of still another embodiment of the invention.

Referring now ot Figure 1, there is shown a conventional electricalinstrument of the permanent magnetmovable coil type that includes amagnet .10 having pole pieces 11, 12 between which is mounted a movablecoil 13 that rotates through an angle which varies with the magnitude ofcurrent flowing in the coil. The coil is carried by axially-alignedshafts rotatable in adjustable jewel bearings. In the interest ofsimplifying the drawing, only the upper bearing 14 is shown. A pointer15, affixed to the movable coil, moves over a calibrated scale 16 on thescale plate 17. Spiral springs, such as the spring 18, provide themechanical torque to return the pointer to its zero position relative tothe scale when current is not flowing in the coil, as is well known inthis art.

The above-described mechanism is conventional and is mounted within anenclosing casing 20, made of metal or plastic, that is closed at theupper end by a transparent cover 21 hermetically sealed to the rim ofthe casing. It may here be pointed out that studs by which current isconducted to the movable coil, generally pass through the bottom of thecasing, such studs likewise being of approved hermetically-sealedconstruction.

For numerous reasons, understood by those skilled in this art, it issometimes necessary or desirable to correct the normal zero position ofthe instrument pointer. This is done by rotating a slotted screw 25 thatis part of an assembly having a pin passing within the abutment 26 thatis rotatable about the movable coil axis and connected to one end of thereturn spring 18.

Figure 2, which is a central cross sectional view through thezero-adjusting device, illustrates my novel pressure sealedconstruction, whereby the position of the pointer may be altered,externally of the instrument, without disturbing the hermetical sealingof the casing. The transparent cover 21, shown as a plastic, preferableis provided with a circular bore, or recess, in the inner surface, suchrecess having sections of two different diameters, as shown more clearlyin Figure 3. The small diameter recess accommodates the axial shaft 30of the metallic member 31 and the large diameter recess accommodates aresilient washer 32, made of rubber or other pressuredeformablematerial. The dimensions of the member 32 are such that it is freelyinsertable within the cover recess prior to the final assembly of thezero adjuster mechanism. It will be noted the member 31 has an integral,headed extension 33. Part, or all, of the surfaces of this extension areroughened, as by knurling, so that when it is molded directly into theplastic disc 34 such disc and the metal member 31 will form a strongunit.

In assembling the components of my zero adjuster the resilient disc 32is placed into the recess of the cover 3 21 and the shaft 30 of themetallic member 31 is inserted through the disc opening and into thesmall diameter recess. The slotted member 25' is provided with alongitudinally-knurled, rather than threaded, shank which is forced intothe axial bore 35 in the shaft 30. By means of a suitable tool, suchasan arbor press, opposed pressures are applied to the head of the member25' and to the plastic disc 34 to deform the resilient washer 32 apredetermined amount. Such resilient washer, having its flat surfaceconfined by the recess base and the member 31, will be deformed suchthat it will come into surface contact with all walls defining theresulting cavity between the member 31 (and its shank 30) and theplastic cover 21. When once assembled the resilient washer remainspressure loaded by reason of the gripping action between the knurledshank of the slotted member and the inner wall of the bore in the shank30.

I have found that such pressure loading of the resilient. washer servesasan effective and entirely satisfactory hermetical seal whilepermitting rotation of the entire assembly by a screwdriver insertedinto the slot of the external head. As is apparent, the insulator member34 includes an integral pin 39 which is adapted. to. fit within theabutment 26, shown in Figure 1, whereby rotation of the slottedheadimparts a corresponding rotation tosuch abutment to alter'the positionof. the pointer.

Figure 4' illustrates another embodiment of the invention wherein; theshank of the metallic member 31 extends through the cover 21'. In thiscase the slotted head 36 is provided with an axial bore 37 to receivethe shank end of the member 31. It will be seen that the insulatormember 34' and the head 36 can be. pressed together to apply apredetermined perssurev on the resilient washer 32" andthe parts lockedin such position by a pin 38 that passes through aligned, transverseholes in the shank of the member 31" and' the head 36. In order toobviate the need for maintaining close tolerances, the transverse holesthrough the head 36 and the shank of the member 31 may be drilled as asingle operation while the parts are restrained under proper pressure.

To facilitate rotation of the zero adjuster mechanism some or all ofthose surfaces subject to relative movement during rotation oftheslotted screw, or head, may be given a light coating of a suitablelubricant.

In the Figure embodiment of the invention the internal member of thedevice comprises a single disc 40, made of a suitable insulatingmaterial having good mechanical strength, having an integral extensionthat includes an axial bore therein. The longitudinally-knurled shank ofthe headed member 25' is force fitted into such bore a proper distanceto subject the resilient, washer, 32 to a predetermined pressure,deformation. As. shown in Figure 6', the member 40 includes radial slots41. extending from a central recess, 42, such slots. adapted to. en-

gage, the. abutments. of the instrument mechanism, as is.

well known in. the instrument art,

Figure 7 illustrates. another embodiment of my inventi'on which issomewhat similar to the construction illustrated' in Figures. 2 and 3..Here the hole in the cover member 21' terminates in a single,enlarged-diameter bore in the inner surface of the. cover. The body ofthe. metallic member 45 is encased, substantially, inthe insulator mem:ber 46', as by molding, said metallic member including the knurledportions 47 to form a strong unit. The. slotted stud 48 has a shankpassing through the hole in the cover member and into an axial. hole inthe, shank of the metallic member 45. The diameter of the, stud shankis. somewhat larger than that of, the. associated hole in. the shank ofthe member 45 whereby these parts must be forced together and when onceassembled the resilient washer 32 will remain, pressure-loaded withinthe. bore in, the cover.

Figure 8. illustrates a modification. of theFigure 7 constructi'on,Herethemetallicmember 451' does. not include a. shank andv the, shank ofthe slotted stud 4.8,." is forced.

directly into a hole in the body of the member 45. It will beapparentthat in this construction the hole in the cover member 21 can be of asmaller diameter than that required in the construction shown in Figure7.

While the constructions illustrated in Figures 7 and 8 show aneccentric, integral pin 49 for transmitting rotary motion of the zeroadjuster to. the instrument movable coil, or other member, disposedwithin the instrument casing, it will be apparent that such pin may bereplaced by a slotted type of coupling arrangement as described withreference to Figures 5. and; 6.

Aside from the simple construction of the parts and the assembly thereofand the retention of the hermetical sealing of the instrument, animportant feature of my invention is the complete electrical isolationof the externally-accessible zero adjuster head from the instrumentmechanism by means of the insulator members. There is no difliculty inproviding such assembly to meet. an A C. voltage breakdown test ofseveral thousand volts.

Having now described my invention in detail in accordance with thepatent statutes, various changes and modifications will suggestthemselves to those skilled in this art. It will be apparent the memberdisposed inside the instrument casing, and rotatable upon rotation ofthe external, slotted head, may take a variety of specific forms toprovide a proper engagement between such member and the part to berotated or adjusted. For example, such member may carry a suitable armfor engaging the movable contact of a magnetic contact type relaywhereby the relay contacts may be separated externally of the relaycasing; Also, the specific form of the external portion of the headedmember is a matter of design choice and may take the form of a hexagonalhead, a knurled knob for finger operation or etc. It is intended thatsuch changes andmodifications shall fall within the spirit and scope ofthe invention as recited in the following claims.

I claim:

1'. An arrangement for' adjusting the position of a movable elementdisposed within a casing said arrangement comprising a cover having ahole therein which terminates in an enlarged-diameter bore in the innersurface of the cover, a resilient washer disposed within the said boreand in full surface contact with the wall defining the base of the bore,a clamping member in fiush contact with the washer said member includingan axial bore and engaging means for mechanically coupling the member tothe movable element, and a stud having a head abutting the outer surfaceof the cover and a shank passing into the axial bore in the clampingmember.

2. The invention as recited in claim 1, wherein the stud shank is forcefitted into the axial bore in the clamping member, and the said engagingmeans comprises an eccentricv pin extending from the clamping member.

3'. An arrangement for adjusting the position of a movable elementdisposed within a casing said arrangement comprising a cover having ahole therein which terminates in an enlarged-diameter bore in the innersurface of the cover, a resilient washer disposed within the said bore,a metallic member including a shoulder abutting the washer and a shankhaving an axial bore therein and passing through the washer, aninsulator member secured to the metallic member and including engagingmeans for mechanically coupling the insulator member to the movableelement, and a stud having a head abutting the outer surface. of thecover and a shank passing through the cover hole and into the axial borein. the: shank of the metallic member.

4. The invention as recited in claim 3, wherein the said insulatormember is molded on to the said metallicmember and includes a fiatportion abutting the said. Washer.

5. The invention as recited in claim 4, wherein the said engaging meanscomprises an eccentric pin extending from. the said insulator member.

6. An. arrangement. for adjusting the position. of a movable elementdisposed within a casingsaid arrangement.

comprising a cover having a hole therein which terminates in anenlarged-diameter bore in the inner surface of the cover; a resilientwasher disposed within the said bore; a clamping member comprising ametallic member molded in an insulator member, said metallic andinsulator members including contiguous, mono-planar surfaces abuttingthe washer and said insulator member including engaging means formechanically coupling such member to the movable element; and a metallicstud having a head abutting the outer surface of the cover and a shankpassing through the cover hole and the washer and into a bore in thesaid metallic member.

7. An arrangement for adjusting the position of a movable elementdisposed within a casing, said arrangement comprising a cover having asmall diameter hole extending in from the outer surface of the cover, anintermediatediameter bore communicating with the said hole and with anenlarged-diameter bore formed in the inner surface of the cover, aresilient washer disposed within the enlargeddiameter bore, a metallicmember including a shoulder abutting the washer and a shank having anaxial bore therein and passing through the washer, an insulator membersecured to the metallic member and including engaging means formechanically coupling the insulator member to the movable element, and astud having a head abutting the outer surface of the cover and a shankforcefitted into the axial hole in the metallic member.

8. The invention as recited in claim 7 wherein the said engaging meanscomprises a radially-extending slot in the outer surface of theinsulator member.

9. The invention as recited in claim 7 wherein the said engaging meanscomprises an eccentric pin extending from the insulator member. 1,

10. The invention as recited in claim 7 wherein the shank of the saidmetallic member extends into the intermediate-diameter bore of thecover.

References Cited in the file of this patent UNITED STATES PATENTS1,661,214 Carpenter Mar. 6, 1928 2,413,414 Obermaier Dec. 31, 19462,440,392 Butler Apr. 27, 1948 2,513,184 Lamb June 27, 1950 2,560,879Lamb July 17, 1951 2,654,070 Lamb Sept. 29, 1953

